With the increasing spread in electronic commerce, there has been a commensurate increase in electronic copying technology. Digital copy technology such as DVD-R, DVD-RW, CD-R and CD-RW is now widely available. In addition, paper copying machines, facsimile machines, and electronic scanners have long been available. Ensuring the protection of electronic and printed media from unauthorized copying and modification continues to become more important as electronic commerce continues to spread into every area of the national economy.
Data hiding is one form of content protection that is sometimes employed for copy control and copyright protection. Embedding of data such as a watermark onto a host medium or image is one example of data hiding. An embedded watermark is typically intended to provide copyright control and/or access control of a product.
Suitable methods for embedding watermarks in images are known for color or gray scale images that contain a substantial amount of texture. These methods rely upon the human eye's ability to tolerate noises in high texture regions of an image. One such technique utilizes a Just Noticeable Difference (JND) function to determine where information can be hidden in an image. The JND function may, for example, lead to the embedding of watermark information in a region of a portrait that depicts hair. Without the JND function determination, the watermark may be embedded in a region of the same halftone portrait that depicts the face of the subject. Because the human eye is sensitive to noise in smooth regions of an image, the latter case is likely to result in easily observed visible artifacts.
Although many images have sufficient texture to hide an embedded watermark from human eyes, there are types of images, such as comic strips and clip art images, that do not have sufficient texture for this purpose due to their relative simplicity. Many of these images are simple compositions of groups of smooth regions that cannot withstand the “noise” added by known watermarking techniques without perceptible degradation. Thus, not many copyrighted low texture images have been provided with watermark protection.